1. Field of the Invention
The present invention concerns a method of preparing an alkali metal diffusion-preventive layer comprising a silicate glass layer at the inside of a substrate such as a Si substrate and silicate glass substrate by using an ion implantation method and, more in particular, it relates to a method of preparing a phosphor silicate glass layer having a performance for preventing high alkali metal diffusion.
2. Description of the Prior Art
Inorganic glass with improved surface property by implantation of ionized phosphorus from the surface has been known in, for example, Japanese Patent Laid-Open Sho No. 56-84344 and Sho No. 56-116034. Further, as a method of manufacturing glass plates for producing semiconductor device, there has been known a method of ion implantaion of phosphorus to the surface of a glass plate made of an alkali metal containing silicate glass, applying heat treatment, further implantation of nitrogen ions and then applying heat treatment again by, for example, Japanese Patent Laid-Open Sho No. 63-222046.
The method of ion implantation of phosphorus to the surface of the glass plate and applying heat treatment as described above has a merit of forming an apparent phosphor silicate glass layer at the inside of the glass plate thereby enabling to improve the surface property of the glass plate, but the effect of preventing the diffusion of alkali metal to the surface of the glass substrate (so-called gettering effect of the alkali metal) can not be attained as expected and there has been a problem that the gettering site is not efficiently formed on account of insufficient oxidation of implantated phosphorus.